The invention relates to the continuous casting of metals. More specifically, it relates to casters for casting thin metal strip directly from liquid metal, of the type called xe2x80x9ctwin-roll castersxe2x80x9d.
These casters comprise, in the usual manner, two rolls having horizontal axes, the cylindrical lateral surfaces of which are placed side by side at a minimum distance corresponding to the thickness of the strip that it is desired to obtain. They thus define a casting space which is closed off laterally by two plates made of refractory material, called xe2x80x9cside wallsxe2x80x9d, mounted on a rigid metal baseplate and applied against the plane ends of the rolls. The peripheral surfaces of the rolls are made of a material having a high thermal conductivity (such as copper and copper alloys) and are internally cooled in a vigorous manner.
Each of these side walls is held in position by means of an assembly generally comprising a plurality of members which press it against the rolls with a force at least sufficient to prevent liquid metal from exfiltrating from the casting space. These members are mounted on a frame and comprise rigid rods which are fastened to the rear face of the baseplate to which the side wall is fastened and which are mounted on thrust springs, or controlled cylinders, or a combination of spring-loaded rods and controlled cylinders. These thrust members are, for example, three in number, distributed in the following manner. One of them exerts its action in the longitudinal mid-plane of the side wall and in its lower part, at a level close to the nip, that is to say the region where the rolls are closest together. The other two thrust members exert their action in the upper part of the side wall, at symmetrical points with respect to its longitudinal mid-plane. The thrust forces are thus distributed over the side wall so that a pressure sufficient to prevent exfiltration of liquid metal from the casting space can be exerted on all the regions of contact between the side wall and the ends of the rolls. However, this pressure must not be too high for fear of causing rapid wear of those parts of the side wall which rub against the rolls, which would severely limit the duration of the casting run. Documents JP-A-04322849 and EP-A1-0698433 are representative of this prior art. The thrust members and their means of connection to the frame and to the side wall are all identical thereto.
Because of the high temperature of the liquid metal (about 1500 to 1550xc2x0 C. in the case of steel), the members for supporting the side walls are subjected to intense thermal stresses. It is therefore necessary to cool at least the baseplate, by means of an internal circulation of water, so as to limit the deformations and expansions of the support members. However, it is not possible to completely eliminate the expansions, and experience shows that even minute expansions can disturb the operation of the thrust members. This is particularly so when these thrust members consist of controlled cylinders which are more rigid than spring-loaded rods and therefore less able to damp the variations in the position of the points on the side wall against which their forces are mainly exerted. These expansions that the thrust members must absorb can falsify the information that they receive and the actions that they transmit to the side wall, or may even contribute to damaging them.
The object of the invention is to propose a design of a device for holding and applying the side walls against the end faces of the rolls, allowing the thrust members to exert their action without this being disturbed by the differential expansions of those parts of the device that are exposed to a high temperature.
For this purpose, the subject of the invention is a device for applying a side wall of a caster for the continuous casting of thin metal strip between two rotating cooled rolls having horizontal axes against the plane faces of the rolls, of the type comprising three thrust members connected to a frame held in a fixed position, which exert their actions on the rear face of a baseplate to the front face of which the side wall is fastened or on the rear of the side wall, the said action being exerted via means for connecting each of the said thrust members to the said baseplate or to the side wall, characterized in that the said means for connecting a first thrust member allow translational relative movement between the said thrust member and the baseplate or the side wall both in a horizontal direction parallel to the plane of the plane faces of the rolls and in a vertical direction parallel to the plane of the plane faces of the rolls, in that the said means for connecting a second thrust member allow translational relative movement between the said thrust member and the baseplate or the side wall in a horizontal direction parallel to the plane of the plane faces of the rolls and in that the said means for connecting the third thrust member allow no translational relative movement between the said thrust member and the baseplate or the side wall.
Preferably, the first thrust member exerts its action on the lower part of the baseplate or of the side wall, while the second and third thrust members exert their actions on the upper part of the baseplate or of the side wall.
As will have been understood, the invention consists in connecting the baseplate supporting the side wall (or the side wall itself if no baseplate is used to support it) to the three thrust members while allowing two of the three connections the possibility of moving in a plane parallel to the plane of the plane faces of the rolls against which the side wall is applied, from a point kept fixed. In this way, the baseplate or the side wall can expand freely without this expansion disturbing the actions of the thrust members, and good rigidity of the linkages between the various parts of the side wall and its support means is maintained. In particular, the action of the lower cylinder is made independent of those of the two upper cylinders and the actions of the two upper cylinders are made independent of each other.
The invention will be more clearly understood on reading the description which follows, given with reference to the single appended figure, which shows schematically, seen in perspective, an example of a device for applying a twin-roll caster side wall according to the invention.
The side wall 1 made of refractory material is fastened to a metal baseplate 2 and applied against the plane ends of the casting rolls (the outlines 3xe2x80x2, 3xe2x80x3 of which are shown by the dashed lines) by the device which will be described below. The side wall 1 and the baseplate 2 are illustrated very schematically, the precise way in which they are constructed being of no importance to the invention. The rest of the description will be given with reference to a coordinate system Oxyz in which the directions Ox and Oz are respectively the horizontal and vertical directions lying in the plane defined by the plane faces of the rolls or by the side wall 1 and the direction Oy is the horizontal direction perpendicular to the said plane, and therefore parallel to the axes of the rolls.
The device for applying the side wall 1 according to the invention comprises a fixed frame 3. This frame 3 is mounted on a movable trolley (not illustrated) which allows it to be moved, as required, closer to or further away from the rolls, when positioning the side wall 1 before the start of the casting run and removing the side wall 1 after the end of the casting run. The frame 3 and the baseplate 2 are connected by means of three controlled cylinders 4, 5, 6. The first cylinder 4 exerts its action in the longitudinal mid-plane of the side wall 1 and in its lower part, at a level close to that of the nip 7. The second cylinder 5 and the third cylinder 6 exert their actions in the upper part of the side wall 1, at symmetrical points with respect to its longitudinal mid-plane, to the left and to the right of the said plane, (in the example illustrated). These cylinders 4, 5, 6 are controlled, in a known manner, by a device (not illustrated) comprising computing means which govern the movements of their respective movable rods, so as to move them closer to or further away from the rolls, and the forces applied to the same rods. As is conventional, the cylinders 4, 5, 6 may be controlled in accordance with the intensity of the forces absorbed by the said movable rods 8, 9, 10 during application of the side wall 1 against the rolls, by means of the information gathered by sensors designed for this purpose.